1. Field of the Invention
This invention relates to printers which place a series of dots on underlying media to form a pattern, alpha numeric symbols, or a bar code. It relates more to those types of printers which are thermal printers wherein a print ribbon having a wax or other displaceable material thereon can be heated and disposed on an underlying media for printing thereon. Such underlying media can comprise paper, plastic, a web supporting a plurality of labels, or other media. The invention specifically relates to the print ribbon transport in a consistent manner to avoid various printing inconsistencies. Such printing inconsistencies can be light or dark print, improper alpha numeric symbols, or fuzzy printing as well as bar codes having either unclear or improper separations.
2. Description of the Prior Art
The prior art of thermal printers relied upon various brakes, clutches, supports, and other apparatus in order to provide for the proper transport of the print ribbon. The print ribbon has material thereon such as a wax or other type of heat sensitive material which can be used to imprint underlying media. The print ribbon has a very flexible and thin consistency. It borders on the fineness of a film like material of a flexible plastic sheet. Thus the print ribbon web should be maintained in a uniform and consistent position with respect to the web.
Disposed on the print ribbon is the print substance which must be disposed on underlying media. The substance of the print ribbon which is disposed under heated conditions is placed on the underlying media. It is placed at discrete points that must be accurately maintained. The accuracy is with regard to alpha numeric representations and particularly with regard to bar codes which have to be properly read.
During the process of displacement of the substance from the print ribbon, a heating element is used. The heating element can be an elongated bar having very discrete heating elements that conform to a certain number of dots per inch as desired. Such dots per inch in the way of heating elements can range up to 300 dots per inch and more.
The print ribbon when passing under the heating element or printer head and on top of an underlying media and before and after is subject to wrinkling, striations, displacement, stretching, and other distortions. This is caused by tension, inertia, and other elements in the drive systems. In the past, it has been customary to compensate for these distortions with various clutches, controls, and supports. These mechanical elements which although workable in some cases did not always provide the best results. The distortions even after passing through the printer head are propagated backwardly to the printer head.
Further complicating this matter is the fact that the underlying media that is to be printed on must be driven over a platen which is a rotatable platen formed of a hard elastomeric material against which the print ribbon is guided and heated by the heating elements of the print head. Oftentimes, the print ribbons become mis-matched with the underlying media, and distortions occur in a bar code which can be quite severe.
This invention utilizes a positive drive system for the print ribbon by a pair of D.C. brush motors that drive the take-up and supply spools. The motor velocities are measured by circuits that measure the Back EMF (BEMF) voltage of the motor drives. The movement and monitoring of the print ribbon can then be derived from the spool radius and the motor torque, as well as inertia and other dynamic aspects including the mass of the rolls on both the take-up and supply spools.
In order to maintain a print ribbon web without striations, stretched areas, or ridges and valleys, this invention incorporates a unique transport system for the ribbon. This includes spring biased rollers in order to remove ribbon distortions. Also in order to balance the edges of the ribbon a gimbaled support that can be a roller is provided.
An object of this invention is the control of the tension, movement and consistency of the print ribbon web. It is particularly important as it passes through the print head and over the underlying media that is to be printed.
A further enhancement is that the ribbon tension can be varied and maintained as to differently sized ribbon widths. The tension and movement is maintained on the print ribbon by means of rollers and a gimbaled or pivotal support.
An object of this invention avoids prior art deficiencies by lessening print ribbon wrinkle. This is enhanced by rollers, and proper support across the width of the print ribbon web.
Another object of this invention is that it provides for tensioning and uniformity across the width of the print ribbon web. When prior art mechanical devices are used to maintain tension, especially friction type devices, another mechanism needs to be added to maintain the tension. This is usually a spring wrapped around a hub. This invention removes the need for this additional mechanism.
The invention provides rollers or other surfaces mounted on springs and/or gimbals or pivots which help to remove plastic ribbon set, striations, wrinkles, and inconsistencies from the ribbon. This is accomplished by working and guiding the ribbon in two different directions as it is taken off the feed spool, and balancing support across the width of the ribbon.
The support of the ribbon across its width is enhanced by a gimbaled or pivotal support that can be a plate, rod or roller. The center pivot of the gimbal can be adjusted by a motor or manually to accommodate various widths and edge dimensions of the print ribbon.
In summation, this invention is a thermal printer and transport system having rollers which help to remove plastic print ribbon inconsistencies from the spool while maintaining tension, proper movement, transport, and a smoothing effect to the print ribbon with a gimbaled or pivotal support for accommodating support across the width of the print ribbon.
More specifically, the invention comprises a print ribbon transport system which helps to remove ribbon inconsistencies and variations. Ribbon variations are encountered due to the fineness of the print ribbon and heating that takes place at the thermal printer head. In order to remove the variations this invention utilizes a pair of rollers or other offset surfaces. The rollers specifically work the print ribbon in one direction and then the reverse direction. This reversal of direction and the working of the print ribbon irons the print ribbon in a manner so that wrinkles are diminished.
The invention further incorporates the concept of eliminating variations by working the print ribbon over a roller or another type of reverse surface. This working can be enhanced by variable spring loadings on the ribbon through leaf coil springs or other means supporting rollers or other working surfaces such as rods or plates across which the print ribbon moves.
The invention enhances the further handling of the print ribbon after and during the movement thereof through the print head process by means of another transport system. This second transport system after printing incorporates a roller or guide surface which can be gimbaled to accommodate variations across the width of the print ribbon. This gimbaled roller can be provided with any other type of surface so as to accommodate the movement of the print ribbon thereacross.
A further feature of this invention is the ability to adjust the placement of the gimbaled support with regard to its overall lateral support of the print ribbon. This is accomplished by a screw means or other adjustment means that can move the center of support of the print ribbon gimbal or gimbaled roller laterally across the print ribbon both manually and automatically.
A further enhancement of this invention is the fact that it can accommodate variously sized and variable print ribbon width by having a motorized adjustment of the support of the print ribbon after it has been printed upon. This can be done by a motorized screw system such as a lead screw and/or ball screw with a motor and a sensing system that senses the edge regions of the print ribbon.
A further feature is the adjustment of the print head pressure by a motorized movement of the print head against the platen.
As a consequence, this invention is a significant step with regard to the transport of print ribbon, the ability to diminish print ribbon variations, inconsistencies in print quality, and the ability to make adjustments of variably sized print ribbons.